The invention relates to a control system for multi-color rotary printing machines, for example for alternative one-side and two-side printing.
One such control system is disclosed in German Democratic Republic Pat. No. 89115 and in corresponding U.S. Pat. No. 3,818,827. In that control system, the printing stations or individual functional units of the printing stations are activated in the proper sequence and with the proper timing by a control system comprised of a shift register. Each ON or OFF command signal is synchronized with the actual occurrence of the rotation and the phase within such rotation during which the commanded operation is to be performed. With this control system, there is a fixed coordination between certain rotations and phases within the rotations for the respective command signal for activating the associated functional group (e.g., for moving an offset cylinder into engagement with a printing cylinder, etc.) controlled by a signal detector activated by a change of signal of the associated shift-register stage.
With printing machines capable of alternative one-side or two-side printing, a control system exhibiting such fixed coordination cannot in general be employed. With such machines (disclosed for example in German Democratic Republic Pat. No. 54703, and in corresponding British Pat. No. 1,128,087), there occurs during one-sided printing a transfer of the sheet from the printing cylinder of one printing station via a transfer drum to a printing cylinder of the next printing station, with the leading edge (first printed end) of the sheet both times entering into the tangency point between the printing cylinders and the intermediate transfer drum. In other words, the same end of the sheet constitutes the leading end of the sheet both upon entry into the point of tangency between the first printing roller and the transfer drum and upon subsequent entry into the point of tangency between the transfer drum and the second printing roller. When changing over from one-side printing to two-side printing, the length of the path of sheet travel undergoes a change composed of a constant component dependent solely upon machine dimensions and of a variable component dependent upon the sheet format, i.e., upon the length of the sheet in the direction of sheet travel. Accordingly, when changing over from the one-side printing mode to the two-side printing mode, or vice-versa, there occurs a loss of coordination between, on the one hand, those functional units within the printing machine located downstream of the sheet-flipover location, and, on the other hand, the shift-register stages associated with those functional units in the printing mode previously employed. Because the control shift register is usually driven by a train of shifting signals synchronized with the cycles of machine operation (for example revolutions of a main shaft, such as a shaft of the transfer drum or of one of the printing cylinders, or some other rotary component of the machine), it is possible to express the just-mentioned loss of coordination in terms of a phase shift-- i.e., a phase shift between the transfer of a particular sheet-representing signal through the successive stages of the shift register, on the one hand, and, on the other hand, the actual travel of the respective sheet through the now longer or shorter travel path through the machine.
This phase shift, or in other words this change of length of the sheet travel path, can be broken down into two components. The first component is constant in the sense that it is determined exclusively by the dimensions of the machine components and the designed-in changes of relative angular and other positions which are made to occur upon a changeover from the one-side mode to the two-side mode, or vice versa. The second component of the phase shift, or equivalently of the length of the sheet travel path, is variable in the sense that it is determined by the sheet format, e.g., the length of the sheet considered in direction of sheet travel through the machine.
U.S. Pat. No. 3,654,861, to Rudolph et al., issued Apr. 11, 1972, presents a detailed description of the sheet flipover action. That description makes particularly clear exactly why and to exactly what extent the length of the sheet travel path alters upon a changeover from the one-side printing mode to the two-side mode, or vice versa, and also makes clear why the path length change can be considered to consist of a constant and a variable (sheet-format-determined) component. The entire disclosure of U.S. Pat. No. 3,654,861 is incorporated herein by reference.
Such phase shifts or changes of length of the sheet travel path can also arise from the introduction of a working station into the sheet travel path for special purposes, for example a sheet-processing station such as an additional printing station for printing an additional image or image component, a drying station, or the like. If an additional working station is inserted, then in the illustrated embodiments one disconnects those of the signal detectors 19 which are affected and reconnects them, for example, further down along the shift register. Additional shift-register stages need not be used.
German Democratic Republic Pat. No. 94400, corresponding British Pat. No. 1,320,282, and corresponding co-pending U.S. patent application Ser. No. 414,536, filed Nov. 9, 1973, disclose the expedient of compensating for the above-described phase shift or change of length of the sheet travel path by resorting to an intermediate shift register which by means of electrical switches can be inserted into the main shift register between two stages of the main shift register to add to the length of the main shift register and which, conversely, can be removed from the main shift register to shorten the latter. The disadvantage of that expedient is that additional shift register stages are required, and the cost of these additional stages and of the means for effecting their control is fairly considerable. Also, the control arrangement, because it in effect comprises two alternative shift-register control systems, does not have a unitary circuit configuration.